Automatic telephone-exchange



A. M. BULLARD.

AUTOMATIC TELEPHONE EXCHANGE.

APPLICATION FILED MAR.12. 190s.

1,327,805. Patented Jan. 13, 1920.

6 SHEETS-SHEET l.

Aff@

A. M. BULLARD. AUTOMATIC TELEPHONE EXCHANGE.

' l APPLICATION FILED MAR-12 |906. 1,327,805.

A. M. BULLARD. AUTOMATIC TELEPHONE EXCHANGE.

I APPLICATION FILED MAR. l2. T906. 1,327,805. Patented Jan. 13, 1920.

6 SHEETS-SHEET 3.

A. M. BULLARD.

AUTOMATIC TELEPHONE EXCHANGE. I

'APPLICATION FILED MAR. 12, 1906. l 1,327,805, Patented Jan. 13, 1920.

6 SHEETS-SHEET 4.

A. M. BULLARD.

AUTOMATIC TELEPHONE EXCHANGE.

APPLICATION FILED MAR. I2, 190e.

1,327,805, Patented Jan. 13, 1920].

6 SHEETS-SHEET 5.

A. M. BULL-ARD.

AUTOMATIC TELEPHONE EXCHANGE.

APPLICATION FILED MAR. 12, |906.

1,327,805. Patented Jan. 13, 1920.

units selector.

ALBERT M. BULLAED, CF NEW Yonx,` N. Y., WESTERN ELECTRIC COMPANY, INCoEPo ASSIGNOR, BY MSNE ASSIGNMENTS, TO

RATED, A CORPORATION OF NEW YORK.

AUTOMATIC TELEPHONE-EXCHANGE.

Specification of Letters Patent.

Patented Jan. 13, 1920.

Application led March 12, 1906. Serial No. 305,548.

To all whom 'it may concern:

Be it known that I, ALBERT M. BULIARD, citizen of the United States, residing at New York, in the county of New York and State of New York, have invented a certain new and useful Improvement in Automatic Telephone-Exchanges, of whichthe following is a full, clear, concise, and exact descri tion.

y invention relates to an automatic telephone exehange system arranged to accommodate a large number of lines, for example, ten thousand, and its object is to provide an improved organization of circuits and apparatus by which the selective switching of any two subscribers instruments into connection with each other may be accomplished rapidly and with certainty, while meeting the various requirements of signaling, prevention of interference with busy lines, good telephone transmission and economy of current consumption.

My invention contemplates an exchange provided with hundreds selectors, and tens-and-units selectors for making connection between a calling and called line under the control of the calling station. Each line in the exchange terminates upon a number of groups of contacts, each group with-its Contact arm and the mechanism therefor being designated as a tens and Each line also has at the central ofiice a distributer individual thereto, which is adapted upon the closure of the substation switch of such line to automatically connect the line with an idle hundreds selector. Each hundreds selector is provided' with contact-s representing the hundreds digits of the lines in the exchange, and the subscriber at a calling station is provided with means for operating the selector connected therewith by the distributer, to bring the selector into connection with anyhundreds contact, to connect the calling line with the Contact representing the hundreds digit of the line with which connection is desired. The distributer when operated disconnects from the calling line the terminals representing such line upon the' tens and units selectors, and applies thereto a source of test current, said terminals remaining disconnected until the distributerl is returned to its normal position.

The vcontact representing the hundreds digit of the called line is connected with a finder which is operated when a calling line 1s connected to such hundreds digit contact to connect said and units selector, such tens and units selector being adapted to be operated from the calling station to connect the calling line with the terminals of the called line. The calling station is equipped with a ringing key adapted to apply ringing current to the called line. When the tens and units selector makes connection with the terminal of the called subscriber, a test potential is applied to the remaining terminals of such line.

After conversation is terminated, and the subscribers hang up their telephones, the apparatus is automatlcally returned to its normal position.

In case the called line were busy, the two selectors and the finder for selecting an idle .tens and units selector would be immediately returned to their normal positions and a source of busy tone current applied to the calling line, the mechanism associated with its distributer remaining operated, since it is under the control of the calling station. Thus, if the calling subscriber is slow in comprehending the lbusy signal, and is slow in hanging up, his individual distributer is tied up', but no common selectors. Each hundreds selector is adapted to make connections for a given number of subscribers, for example, ten, and each distributer may have, say, five trunk lines, one leading to the hundreds selector apportioned to it, and the other four running to other trunk selectors, so that in case of two or more simultaneous outgoing .calls from. a group of subscribers associated with one hundreds selector, other hundreds selectors are available.

A feature of the invention lies in the improved organization of circuits and apparatus whereby a central source of currentsupply may furnish energy to all the lines, and whereby the required switching, testing and other operations are performed without requiring more than two main conductors for any line or trunk, or more than two sets of multiple terminals for any circuit. That is to say, there is not required a special set of test-terminals and private normal for each line'or trunk, as the two main line-terminals (multipled where necessary) are sutiicient. It has -been usual heretofore in automatic contact with an idle tens exchanges to provide a selector individual to few of the more expensive selectors being required to handle the calls for a large group of lines, an idle selector being automatically secured by the distributer of any line when the line is taken for use.

I will describe my invention more particularly by reference to the accompanying drawings, which illustrate the preferred embodiment thereof, the particular features which I deem novel with me being set forth in the appended claims.

Figures 1, 1a, 1b, 1, considered together represent diagrammatically the complete circuits of twoV connected subscribers. In association with each of these figures is a supplemental diagram indicating means for operating certain contacts which upon the supplemental diagrams are indicated by the same reference letters that appear upon the corresponding contacts shown in the circuits.

Fig. 2 is a simplified diagrammatic representation of the talking circuit of a completed connection; and

Fig. 3 represents in outline the trunking system employed in my invention.l

Referring Iirst to Fig. 3. I have shown three groups of subscribers, eachl associated with a hundreds selector. In the present case I have shown ten Subscribers to a group, but it will be understood that any number desired may be included. Each subscriber is provided with a distributer a having trunk lines a extending to the hundreds selectors, three of which are shown. Each group of subscribers is provided with a hundreds selector for its own especial use, onel trunk line leading from each distributer of the group to the hundreds selector H. The hundreds selector is provided with contacts representing the hundreds digits of the lines in the exchange, and each hundreds contact is connected with a `finder E provided with trunk lines running to the tens and units selectors B, each such selector having associated therewith terminals representing the tens andunits associated with the partielllar hundreds digit terminal with which its finders are associated,-that is, the hundreds contact 49 would beconnected with a finder provided with trunk lines leading to tens and units selectors having terminals 4900 to 4999.

Writh this brief outline of the trunking system, I will now proceed to describe the apparatus and circuit connections at the substation and central oiice in detail. In the drawings Figs. 1, 1c, I have shown two subscribers lines, A, for example, No. 400, which we will designate'the calling line, and B, No. 4899, for example, which We will designate the called line, both extending to their multiple line terminals at the central office. Since the substation apparatus of both lines would be the same, and their Icentral oiiice connections the same, I have simply shown the connections at substation A.

The operating mechanism of the hundreds selectors and tens-and-units selectors may be similar to that ofthe selectors shown in the prior patent to myself and M. C. Borty, No. 709,740, dated September 23, 1902.

Substatz'on equipment.

The subscribers station equipment includes, in addition to the usual telephone apparatus, an interrupter C, which by two successive manipulations controls the operation of the hundreds and of the tens and units selectors as will be hereinafter explained. The interrupter forms no part of the present invention, being a well known type. The apparatus and circuits vof the interrupter will be described in detail hereinafter in connection with the hundreds selector.

tweemaalv (tamtam.

As before stated, each line is providedat the Central oiice with a distributer d individual thereto, adapted to automatically connect the same with an idle hundreds selector in response to a call. Each distributer comprises a set of contacts a2 connected by trunk lines a with a number of hundreds selectors, the first contact being preferably connected with the hundreds selector apportioned to the group of lines containing the line to which the distributer is individual. An arm a3 is arranged to trail over the contacts of the selector. As shown in the diagram, there are two distributers, one for each limb of the line, but it will be'undery lbroken at the central office, but is ada ted to be closed to connect the line with t e distributer by a rela b. At the central office the battery D is 1n a bridge 3 of the line, being grounded at its middle point by a con ductor 4, a relay c being included in said bridge between the positive pole of the battery and the limb 1 of the line,while a relay c is included in said bridge between the negative pole of the battery and the limb 2 of the line. The armature c2 of relay c is connected by conductor 5 with the bridge 3 between the battery D and relay c, and the front contact c3 of the armature is connected with conductor 6, which extends through the stepping magnet d to thefront contact e of a test relay e, a branch 7 extending from said conductor through a retaining magnet f to the negative pole of battery D, said conductor also including the armature and back contact of a relay g, which, however, is not concerned in the operation of calling. The stepping magnet d is adapted to operate an arn'iature d which carries a pawl adapted to engage the teeth of a wheel cl2 carried by the shaft to which the contact arms a3 a4 are connected, and the retaining magnet f is provided with an armature f carrying a detent adapted to engage the wheel and maintain it in an operated position. The armature f is connected by a conductor 8 with the back contact b2 of armature b of magnet b, said armature being included in the portion of line vconductor 1 connected with the arm a3. The armature f of the retaining magnet is provided with a front contact f2 connected with a conductor 9 leading to earth through the test relay e. The armature of the testing relay is connected by a conductor 10 with the negative pole of battery D by means of conductor When the subscriber removes his telephone from its hook to initiate a call, a metallic circuit 1, 3, 2, is completed, including battery D and relays c c. Relay c, in drawing up its armature completes a circuit 3, 5, 6, 7, 3, including battery D and retaining magnet f, which connects the test relay e with the distributer arm a3 by means of conductors 1, 8, 9. Now if the hundreds selector connected with the first trunk line of the distributer a. is engaged, there will be a potential at the first contact a2 furnished by a battery associated with the other calling line, and referred to later, and the relay e will be energized, drawing up its armature and completing a circuit 3, 5, 6, 10, 7. 3, including the stepping magnet d. The magnet (l thereupon attracts its armature (Z, and by means of a ratchet and ratchet wheel operated thereby, advances the distributer springs f1.3 fr* one step to the next pair of Aterminals connected with the second trunk line. The spring a3, in passing between the terminals, momentarily opens the test circuit through relay e, which thereupon releases its armature. If the second pair of terminals leads to a hundreds selector that is already engaged, currentl again" energizes the test relay, and the operation of the stepping magnet is repeated, and continues to be repeated until an idle selector trunk is reached. when the.test relay c remains denergized and the stepping magnet d settles back into resting adapted when retracted to close contacts d connected by a conductor 12 with conductor 7, said conductor 12 including the relay b. Thus when the relay c is energized, and magnet d denergized, a circuit 3, 5, 6, 11, 12, 7, 3, .vould be completed for the magnet b, which, when energized, completes the continuity of' conductors 1 and 2, connectingl the same directly with the springs a3 a4 of the distributer. However, during the rapid vibrations of the armature of the stepping magnet d, the contacts d3 are agitated to such an extent that insufficient current passes through them to operate the cut-0H'l relay 6,' but when the armature of relay al comes to rest in its backward position, an increased amount of current passes through and operates the relay b, which thereupon opens the test circuit of relay e at contacts b b2, completing the circuit 1, 2, for voice transmission at contacts b b3 and b4 b5 respectively. To increaseV the working mar- -gin between non-operating and operating currents, the relay b may be rendered sluggish in any of the well known ways, as by a heavy closed secondary winding, or kthe contacts cl3 may be weighted andspringsupported, or both plans may be adopted.

The cut-off relay b, by opening the circuits of the test relay and stepping magnet, prevents further progression of the distributer arms a3 a, the retaining magnet f by means of its detent, maintaining 'the distributer arms in their advanced position as long as relay c remains energize The rotary movement of the shaft of the distributer opens contacts a a7 to separate the line of subscriber A from the multiple terminals'A of limb 2 of the line. The distributer shaft also separates spring as from its contact anvil a, which is connected with line conductor 1, and moves said spring as into connection with contact am, which is connected with a grounded source of busy test current D', said spring as being connected with the test terminals A of the line to station A, said test terminals constituting the multiple terminals of limb 1 ofthe line.

Let us assume that the sixth pair of terminals a2 a. has been secured, and that from them runs a trunk a a to the hundreds selector H shown in Fig. 1.

Il'zmtZW/s selector.

As before stated, a number of hundreds selectors are provided, each capable under average conditions of transmitting the calls origmatmg from a group of the subscribers,

each selector having a trunk linev running from its Contact arm in multiple to'a number of subscribers distributers. Each hundreds selector is provided with contacts h representing the hundreds digits of the lines of the exchange, and with a contact arm h adapted to be moved over the contacts h by a stepping magnet z', and be drawn down into connection with the desired contacts by a connectin magnet le. It will be understood that tie contact arm h is provided with two contact terminals adapted to be brought into engagement with a pair of contacts connected with the limbs of a trunk line leadingV to a finder E, but for convenience of illustration I have shown two selectors, one in each limb of the extended line. The contact arm is adapted to be stepped forward above itsterminals, and when the desired one is reached to be drawn into connection'with such terminals by a suitable magnet. The limbs aa of the trunk line or extension of line conductors 1, 2, lead .through normally open contacts of 'a cutoff relay l to the arms h of the hundreds selector.

The hundreds. selector is equipped with relays m m in the bridge 12 of trunk conductors a a, said bridge including/a bat! tery D2 grounded at its middle polnt by a conductor 12a. The relay m is operated the moment the cut-0H relay b associated with i the distributer closes contacts b4 b5, for current thereupon flows from the negative pole of battery D2 through relay m', trunk con ductor a, contact a5, arm ai* of the distributer, contacts bt, b5, of the connecting magnet, line conductor 2, through the substation apparatus, and back over conductor 1 through relay c to the positive pole of battery D. The relay m" is provided with an armature m2 adapted when attracted to close a pair of-contacts m4 insulated from said armature and controlling a short circuit 15 about the normally open springs h2 h3 included in trunk conductor a', thus completing a metallic circuit by way of conductors12, a', 1, 2, a, for the relays m m. The contacts h2 h3 are adapted to be closed together when the `hundreds selector arm is away from its normal position, but are' normally open, so that the contacts connected with the hundreds selector at the several subscribers distributers will not have a potential thereat when the hundreds selector is idle. It will be noticed that immediately upon the energization of relay m associated with a selector with which a distributermakes connection, potential is applied to the multiple contacts a? connected with the trunk conductor a at the several subscribers -distributers with which this particular huni tact will complete a circuit from battery D2 for its test relay c and be moved to the next terminal of the distributer.

The relays m m control the operation of the Steppin and connecting magnets i lc of the hun reds selector. The front contact m5 of relay m is connected by conductor 16 with the bridge 12 of the trunk conductors a a between the positive pole of battery D2 and the relay m, and the armature m6 of'said magnet, which when attracted engages contact m5, is connected with a conductor 17, which leads through the stepping magnet i and a retaining magnet n, in series, through the normally closed contacts k of the connecting magnet 7c, armature 02 and its back contact of a relay o to the bridge 12 between relay m and the negative pole of the battery. The connecting magnet la is in a branch 18 leading from conductor 17 t0 normally open contacts i of the step ing magnet z' connected with conductor 1P?. The stepping magnet z' is provided with an armature controlling said contacts and carrying a pawl adapted to engage a ratchet wheel on'the shaft carrying the contact arms h of the selector in the well-known manner, to step said wheel around and advance the contact arms h', while the magnet fn, is provided with an armature carrying adetent adapted toengage the ratchet wheel to maintain the same in its advanced position.

Thus when contacts m5 m6 of relay m are closed, a circuit 12 16, 17 12 is completed for magnets i n, whereupon the arms h of the hundreds selector are advanced one step. The circuit of connecting magnet lo, as before stated, is controlled by the contacts i', which are closed by stepping magnet when energized. These contacts when rapidly agitated are of high resistance. Agitation is effected by the quick reciprocating connecting magnet c 1s energized to draw the arms h downupon the desired hundreds digit terminals. The fmagnet lf: when ener gized attracts its armature k2, which separates contacts c, engaging the member of said contacts connected with the negative pole of battery D2 and so completing a circuit for itself independent of the contact i. In order to thus step the hundreds selector arm to the desired hundreds digit terminal, it is necessary to alternately open and close the circuit of magnet m', and this is effected by means of the interrupter C at the substation. Let us assume that the number of subscriber B with whom subscriber A desires connection is 4899, as shown in the drawings.

The subscriber A would then be obliged to secure connection with the contact terminals 48 upon a hundreds selector.

The interrupter comprises a toothed wheel d5 arranged to successively' close a pair of contacts d as the teeth of the Wheel pass in succession over the end of one member of said contacts. A controller arm Z7 is arranged to be moved forward loosely upon the axis of the wheel against the tension of a coiled spring, and carries a pawl, which, as the controller arm is returned by the spring after its advance, engages the ratchet wheel d5 to carry the same around with it, whereby the contacts d are made and broken a certain number of times, dependent upon the distance to which the controller arm has been advanced. In practice I provide upon the face plate of the interrupter over which the controller arm travels, aV series of holes, each representing a tooth upon the ratchet wheel, the holes being numbered from 0 to 99. I provide a peg which may be inserted in anynumbered hole, so that by moving the arm until it reaches the peg and releasing it, the ratchet wheel d5 will be operated to make and break the contacts d the number of times indicated by the number of the hole into which the peg is inserte-d. The calling subscribers first act after lifting his telephone from its switch hook is to peg into hole No. 48y of the interrupter, and move the controller arm until it strikes the peg, andf release it, whereupon it ret-urns rapidly to zero. When the controller arm is moved away from its normal position. it first causes the closure vof contacts n n2. Contact n is connected by a conductor 19 with the telephone hook,

and so with limb 1 of the line, while contact n.2 is grounded by conductor 20. The closure of these contacts thus grounds limb 1 ofthe line through the telephone set. This causes relays c and m to remain energized, since they receive current from the upper halves of batteries D and D2 respectively. Contacts 71.3 In* are next connected. contact n3 leading to the normally-open pair of contacts d6 by way ot conductor 21, and contact n4, which is included in limb 2, being at -the same time separated from the Contact 11,5 also included in the line circuit. The metallic line circuit is now interrupted, relays c m remaining energized. however, since they are in a grounded circuit. The opening vof the line circuit causes relays c m to release their armatures. The denergization of relay r" does not effect the distributer arms, because relay c is maintaining the excitation oi the retaining magnet f by means of confacts c2 c3. Relay m in releasing its armature my allows the -hundreds selector to become quiescent ready for the selective operation. it being understood that when relay my was first energized, it .Causesthe stepping magnet i to advance the hundreds selector contact-,ann one ystep,-an incidental movement devoid of significance. When the controlling arm of the` interrupter is released, it returns by means of the spring to` zero, and in returning alternately closes and opens the contacts d, which alternately close and open a grounded circuit 21, 2, a, 12

12, including the relay m. The armature `circle of one hundred terminals. The contacts i remaining closed for an instant, the circuit 12, 16, 17, 18, 1 7, 12', is completed for the connecting magnet k, which draws down the arms t upon the 48th pair of terminals, and also disconnects the magnets i and n from the selector.

Each pair of terminals on the hundreds selector is connected by trunk lines with a finder adapted to connect the same with an idle tens and units selector carrying line terminals representing the tens and units-digits associated with the hundreds digitwhich said pair of terminals on the hundreds selector represents,-that is, the tens and units digits of the 48th hundred group of subscribers lines.

When the co'ntroller arm of the subscribers interruptor arrives at zero, it closes contacts 01,4 'a5 and opens contacts n? n4, I'as well as contacts n 11,2, so restoring the {normal metallic circuit of the line, and disconnecting it from springs de.

Abranch conductor 17a extends from conductor 17 through two pairs of normally open contacts h4 h5, through the winding of the relay Z controlling the continuity of conductors a a leading to the contactselector contact arm la. when away from its normal position, and the contacts h5 are arranged to be closed by the connecting magnetl 1 when energized to complete a connection of contact arms It with the hundreds terminals of a desired line, and Vwhen such connection has been completed a circuit from the negative pole of battery D2 is completed by way of conductors 12, 12', 17, 17", 17", to the positive pole of battery D3 and to ground, said circuit including relay Z. This circuit also includes a pair of high resistance contacts d? controlled by the stepping magnet g of the tens and units lnder, which mmedlately upon the energization of the connecting maonct would be operated to step the contact hrm ot the iinder to an idle trunk, so making and breaking said contacts (Z7 and preventing the operation ot' relay Z until such trunk has been selected.

Teozs-mzcZ-um'ts finder.

As shown in the present case, the 48th pair of terminals is connected by a pan' ot trunk conductors 22, 22, with the finder E, adapted to automatically se-lect an idle tensand-units selector. The finder E is of the same construction aS the distributer a, iudividual to each line, and before described, but for convenience of illustration it is provided with a pair of arms c2 c2 connected with trunk conductors 22, 22", and adapted to sweep over two sets ot' trunk terminals c The nder E is provided yvith a stepping magnet@ and retaininglmagnet q anda test relay g2 controlled by relays p p 1n the bridge 17 b of the trunk conductors cf an. These relaysp p are operated at the same time with relays m m, but since the local circuits of their controlled apparatus are open at the contacts t4-h5 until the Contact arms of theselector are brought down upon the desired terminals, these relays perform no function until that moment arrives` branch conductor 23 extends from the front contact of the armature of magnet p through the test relay g2, back contact Z and armature Z2 of magnet Z to the trunk conductor a', which is lconnectedby arm h. of the hundreds selector With the trunk 22 leading to the arm e2 of the tens and units finder.

The operation of the finder E =is the same as the individual distributer a. It the tensand-units selector to which the irst trunk line terminating on the first Contact e3 leads is-busy, a test potential will be present at i the first contact4 and a current will be passed v by way of conductors 22, a', 23, through test relay g2 to t-he front contact of relay p', andthence through its armature, Which is attracted, to earth. The test relay controls at its armature and front contact the continuity of a conductor 24 leading from the conductor 17a through the stepping magnet g and front contact of relay p back to the conductors 17a near its junction with the bridge 17h, a branch 25 leading from conduct-or 24 through the retaining magnet back to the conductor 17a. Thus when the test relay is excited, it `completes a circuit from conductor 17a (which is connected with the negative pole of battery D2) by Way of conductors 24, 17a and 17", to the positive pole of battery D3, said circuit including thestepping magnet Q. The retaining magnet is in a circuit independent of the selecting magnet, said circuit leading from the negative pole of grounded battery D2 by way of conductors 12,17, 17a, 25, 17,

171 to the positive pole ot grounded battery D3. The contact arms e2 of the finder are thus automatically brought into connection with a trunk line leading to an idle tens and units selector. When this has been Adone the armature of magnet g comes to rest and closes the heretofore high resistance contacts (Z7, whereupon current is permitted to How in the circuit 12, 12', 17, 17, 17", to operate the cut-orf relay Z, thereby completing the continuityof the trunk conduct-ors w a from their contacts on the distrib-uter to the contact arms of the hundreds selector, cutting off theselecting and test relays ofthe tens and units finder; the retaining magnet, however, remaining ensov ergized to hold the finder arms e2 in their i advanced position. From each pair of contacts on the tens and units inder E a pair.

of trunks lead to a selector representing the tens and units associated with the hundreds digit selected, that is, since the 48th pair of terminals has been selected on the hundreds selector, trunk lines lead from such i terminals to a finder having contacts, each pair connected With trunks leading to a selector having terminals representing the lines numbered from 4800 to 4899.

- Teas-amZ-units selector.

being included in conductor 26a between the bridge 27 and the selector. The bridge 27 unites trunk conductors 26, 26a, said bridge including relays s s and a battery D4 grounded at its middle point by a conductor 27, said battery being located between the two relays. As soon as the contact arms of the finder E make contact with the terminals of trunk conductors 26, 26a, a 4circuit for the relay s is completed by Way of conductors 27, 27, 26, 22a, a, line conductor 2, through the substation apparatus and back over limb 1 of the line, conductor 3, to the positive pole of battery D and to ground by Way of conductor 4. The arn'lature s2 of relay s is adapted when attracted to close a CII connection with thehundreds selector and the, individual distributer. The contacts r2 in conductor 26 are arranged to be closed by leading to the finder. i

The tens-and-units selector is provided with .a stepping magnet t and retaining magnet u, and a connecting magnet fu controlled by the relays s s. The conductor 28 extends from bridge 27 between the negative pole of battery D4 and relay s', through the armature s2 and its front contact, stepping magnet t and retaining magnet u in series, normally' closed contacts c 102 controlled by connecting magnet c, armature I5 and its back contact of relay I to the positive pole of battery D4, al branch 29/extending from said conductor through the connecting magnet v anda pair of normally open high resistance contacts fus, back to conductor 28. During the vibration of--the armature t', the contacts Q13 do not remain closed for a sufiicient length of time to permit .theI relay c to be excited, but when the stepping magnet remains steadily-.excited upon the comple- -tion of a connection between contact arms 1f of the tens-and-units selector and the called line, the connecting magnet fvis energized and draws the arms r down upon the contacts of the -called line and disconnects the stepping and retaining magnets from the circuit as described in connection with-the hundreds selector.

The calling subscriber at station A, in manipulating the interrupter arm with the peg now in hole 99, advances the arms r of the tens-and-units selector in precisely the same manner as in the operation of the hundreds,selector already described, that is, he operates the interrupter to make and break contacts (Z6 one hundred times, thereby making and breaking the circuit of relay s one hundred times, and stepping the Contact arms 1' around to the pair of terminals representing line 4899. Each time the relay. sV is energized, a circuit 27 28, 27, is completed for the stepping and retaining magnets t u, and when the arms are opposite the desired terminals and the contacts v3 remain closed, a circuit 27 28, 27 is completed for the connecting magnet lv, which magnet draws the arms r upon the contacts of the desired line, and opens at contacts @"vz the circuit of the stepping and retaining magnets. closing in addition a shunt around said high resistance contacts v3. Conductors 30, 30, lead from the pair of terminals r of the tens-and-units selector to the substation of line B.

In the drawing I have shown the distributer associated with the called line 4899. It is essential that this distributer should not I' be operated when a call is received, and for that purpose means are provided adapted to be operated when'the arms r of the tensand-units selector reach the terminals of a called line to render the distributer of such called line temporarily inoperative. To this end I provide a relay F in a bridge 31 of conductors 30, 30, a condenser being interposed in conductor 30 between bridge 31 and the individual apparatus of sub scriber B at the central office, so that the relay will only be operated when subscriber B is called, but will be unaected when subscriber B is calling. v-The apparatus at the centra-l oflice individual to line B'is precisely the same as that described in connection with line A, a bridge 3 of the conductors 30, 30al containing magnets w w similar to the magnets c c of .line A, a battery D5 being included in Asaid bridge between the two relays, with its middle point grounded by a conductor 3b. paratus of the distributer. contact arms r' descend upon the terminals leading to station B a circuit for relay F is completed from the positive pole of battery D4 by way of conductors 27a, 27, 26, 30,31, 30a, 3a and 3b to the negative pole of grounded battery D5. The armature of relay F in drawing up its armature F, opens l conductor '7a and cuts ol'l the supply of current to the distributer magnets. The relay F is of high resistance and impedance, and is very sensitive and efiicient. Placed in series with-relay w it will opera-te upon a current strength that will fail to operate the latter relay.

The relay F when energized, attracts'its armature F and close a shunt 32 about the magnet w', said shunt containing'an impedance coil Itsl armature F2 when attracted, closes a shunt .33 containing the impedance coil a" about the magnet w, said impedance coil 'being shunted out, however, by a conductor 3-1 whose continuity is lcompleted by the armature 1,02- of magnet wi when said magnet` is denergized. These impedancecoils are introduced into the circuits to provide current of adequate volume for voice transmission from the substation apparatus. To show the need of these impedance coils it is necessary to explain the relation of the various current supply relays to each other and to the whole circuit.

In the drawing, Fig 2, a completed connection is illustrated in so far as its talking circuits are concerned, a single battery being shown for supplying the current for transmission. It will of course be under- These relays control the ap- Thus when the' stood that this single battery may be emp s', also connected in multiple rby the selective operations. On the called Aline there is but one relay on each side of the battery, that is, w and w', belon ing to the distributer of the called line. T ese groups are separated by the condensers X X', so

that each' line receiyes its independent supply of current. Now 1t 1s evident that 'distributer relays fw w. are of the same resistancel as distributer relays c c', but relays fw w are of too great resistance to permit a flow of current requisite for transmission When used independently. For example, assume each of the relays to have a resistance ofv 1000' ohms, which would make the combined resistance of relays c m p s connected in multiple, 250 ohms, as against 1000 ohms of relay w. Now, by adding a 333%; ohm impedance coil in multiple with each of the relays lw fw', the combined resistance of relay w and impedancem, as wellas relay' w and impedance m', is 250 ohms. The position of the high resistance 'bridge relay F is shown in this figure in dotted lines.

Signaling. The next step in the connection 4is the application of ringing current to the line ofl connected by conductor 34 with the back contact of armature s* of relay s', said arma-- ture s4A being included with its normally open front contact inthe trunk conductor 26a, the front contact of armature s3 of relay .s being connected by conductor 35 with a,

rounded ringing generator G.

lVhen the calling subscriber operates the ringing key, he first grounds the limb 1 of his line through contacts y g3, and conductor 20, and next separates contacts y y2, thereby opening the metallic circuit of the line and removing battery from limb 2 and trunk conductors 0511,22a and 26a. This latter action denergizes the relays c mi p s. The denergization of these relays does not restore the selector arms to zero, because the work of holding them in place has been thrown upon relays 0 m p s, and the latter are still energized over a path from batteries D D2 D3 D4 over the limb 1 of the callino subscribers line to ground through the depressed ringing keyy.

Before continuing the description of the ringing operation, I Will explain how each 3 From the front contact mI of armature ms of relay m, the conductor 36 extends through two sets h l1? of normally open contacts to the conductor 17. Contacts h are closed when the .arm h of the hundreds selector is away from its normal position, and the contacts h" are closed by the connecting magnet when energized to complete a connection of the arms h with a desired pair of terminals, so that when said contacts are closed a circuit for the connecting magnet is maintained by Way of'conductors 12, 16, 36, 17, 18, 17 12', independent of relay m. The hundreds selectorarm is thus held in its advanced position by relay m independent of relay m.

The .relay p associated with the tens-andunits inder holds the contact arm e2 of the finder in its advanced position by means of a circuit 17h, 17a, 25, 17, 17, 12, 12a, through the retaining magnet g closed by itsarmature.- f

The relay s of the tens-and-units selector holds up the connecting magnet o of the tens-and-unitsselector in the same manner as the connecting magnet of the hundreds selector is held/up. The armature S5 of relay s is connected by a conductor 37 to the negative pole of battery D4 and the front contact of said armature is connected by a conductor 38 with a conductor 28 which supplies current to the connecting magnet, said conductor 38 including two sets of normally open contact springs 7'3-14. The contacts r3 are adapted to be connected by the contact arm 'fr of the selector Whilev away from its normal position, and the contacts 1** are arranged to be closed by the connecting magnet o when energized to draw the arm 1' down upon the contacts of a desired line, so that a circuit is thereby completed formagnet 'u independent of relay s by Way of con-v ductors 27, 37, 38, 28, 29, 28,27, including battery D4.

lVhen the subscriber A presses his ringing key to ground the limb 1 of the line, the armatures of relay s are retracted, and

since relay s is energized and its armature is attracted, a circuit for ringing current will be completed from the ringing generator G by Way of conductors 35, 34, trunk conductor 26a, through contact arm 1' of the tens and units selector to the limb 30L of the called line, thence through the substation apparatus and back over limb 30 of the line, through conductors 3, 33, 34', to front contact of armature F2 of relay F, which armature is connected With the positive pole of battery D5, and thence to ground. To avoid a disturbance of relay w by ringing current traversing its winding in a shunt path from conductor 26a to battery D5 and ground,

v said relay is polarized and biased, and the ringing current made pulsating in character. As shown in the circuit, negative pulsating current is employed, and relay w, is so related tothe battery 4it is operated by the-former current but not by the latter. Therefore the relay w is not loperated during the ringing. The contacts controlling the short circuit about relay w and the impedance coil m remain closed until the called subscriber answers, when such short circuit is broken, allowing relay wto attract its armature, but under the present conditions, when the line B is a called line, the relay fw acts only as an element in the current supply bridge necessaily to transmission of .current to subscriber The subscribers AA and B may now converse over a metallic circuit extending from the Ysubstation apparatus at' station A by way of conductors 1, a', 22, 26, 30, to the substation apparatus of line B, and thence over conductors 30a, 26a, 22a, a, line conductor 1, back to the substation A.

When the calling subscriber hangs up, the relays c m p s become denergized, and the entire connecting apparatus is restored to its normal condition.

Calling a bday Zine. Should the line of subscriber B have been already engaged when selected andtested by subscriber A, the lineof the latter would have been locked out and connected with the busy signal. Furthermore, the entire train of connections set up by his selective act would have been promptly dismembered and each part returned to its resting position ready for common use, with the exception of the distributer individualv to the line A which Would remain tied up underthe control of the calling station. To this end I provide electromagnetic mechanism associated with the tens and units selectors, which when its selector in response to a call makes connection with a busy line, will automatically render inert the relays c m p s controlling the selectors and distributers, and cause the application of a busy test current to the calling line. The relays referred to are maintained inert until the selector arms controlled thereby resume their normal positions, and until such positions have been resumed the hundreds selector, the tens-andunits finder and tens-and-units selector cannot be secured by another subscriber in the act of selecting. This is obviously necessary, because every piece of selective apparatus must begin its initial operation from zero. The distributer a being a mechanism individual to each line, may remain with its reand ringing current that lay c in its operative position until the subscriber calling either hangs up. or begins a new selection. heard until one of these acts is performed.

' The means which I preferably provide for accomplishing the 'above'referred to results, comprises a relay I assoclated and units selector. Saidrelay is provided wit-h a pair of windings I2 I3 respectively, the winding I2 being included in a conductor 39 extending to an inner contact anvilA z of a switching device a adapted to be operated by the retaining magnet of the tens and units selector each 'time it is energized. This switching device comprises a pair of springs z2 es, connected by a bar of insulation which is adapted to be engaged by the armature of the. retaining magnet u to operate said sprlngs, the spring z2 and its normal resting contact being included in thev trunk conductor 26, and thespring es and its normal restin contact being included in trunk conductor 26a. Each time the retaining and selecting magnets are operated to step the tens and units selector arm 'r forward, the switching device is actuated to connect the spring z2 with contact a', so connecting the magnet I with the arm units selector. The armature I4 of relay I controls a short circuit 4,0 about the relay s, which controls at one point the circuits of the magnets of `the selector B. The armature I*5 of relay I is connectedl with the positive pole of battery D4 and controls at its backcontact a supply of current tothe magnets of theselector B', being adapted when attracted to engage its front contact, which is connected by conductor 41 with the negative pole of said batter to 'provide a locking circuit including windingy I3y of said magnet. The conductor 4:1y includes a pair of contact springs 75 which are closed by the .selector arm 1- while away from its normal with each tens 1' of the tensv and l B, a current flows through the lock-out relay I over one of the following two paths, dependentv upon whether subscriber B has made or received a call. If subscriber B has already ma/de a call, the Contact spring B2, which, with its resting Contact, is normally included in a circuit of trunk conductor 30 leading from one of the terminalsV of the tens and units selector, will have been forced into engagement with itsI contact B3, which is' contacts r2, which connected by conductor 42 with the positive pole of battery D5 in the bridge 3, this spring remaining in such position until the distributer of the line B returnsto its normal position, With such condition, current would flow from the positive pole of groundl ed battery Dls through conductors 3, 42,'30, 26, through springs z2 z of the switching device z, which is operated b y the retaining magnet when energized, thence by conductor 39 through the winding I2 of the test relay I.

In case subscriber B has already received a call, the spring B2 will not have een operated. The' terminal of conductor 30 upon the tens and units selector in use by subscriber A would be connected with battery through the relays c m p s of the subscriber who has already called subscriber B, and current from the positive battery pole will flow over the path outlined through relay'I.

Restoration of tens-and-umts selector.

Y In either case the relay I will be operated, f

and its armature contacts will bring about three results, as follows: First, armature I5 will be disengaged from conductor 28 and deprive the tens and units selector magnets of current, thereby permitting the return to normal condition of they selector arm and the mechanism controlled thereby. Second, armature Il5 when it engages its front contact completes a local locking p circuit through the winding I3 of magnet I by way of conductors 27, 28, 41, 27. This local circuit through winding Is insures the locking up of relay I until the 'selector arm has returned to zero, for thenv and only then will the contacts I and the locking coil I3 be denergized; the denergization of relay I being then brought about by theseparation of springs T5. closed by the selector arm r when away from normal position. Third, the other armature I4 closes a short circuit 40 around `relay s for the purpose already stated of also short circuiting the relays o m p i-n multiple with relay s.

While the tens-and-units selector is restoring its parts to normal condition, the busy test or lockout must not be removed from the terminal of conductor 26 upon the distributer E; and this is accomplished by like contacts 115 are closed so long as selector arm 1' is away from its normal resting position. These lcontacts continue the function previously performed by the short circuit 26b closed by the armature '52 of relay s1. this relay being now inert, since the circuit of said relay wasbroken as soon as the iind'er arm e2 commenced its return movement, all the arms, as before stated, commenci-ng their return movement f simultaneously.

Vhen the arm of the tens-and-units select/ or fr has returned to its normal resting posltlon, contacts?a5 are opened and break the circuit through the locking winding pf test relay I; relay I thereupon releases its Restoration of humdreds selector and tensand-wmts f/nder.

When relays m andA p are short circuited by the short circuiting of relay s, as already explained, the armature m5 in retracting closes a circuit for the magnet o which completes a short circuit 43 about the relays m and p, this short circuit taking the place of the one established by the relay of the tens and units selector, which was destroyed when the finder arm o2 left the terminal of conductor 26; The back contact of the armature m8 of relay fm, is connected by conductor 44 with conductor 14, which extends tO the armature m2 of relay m', the front contact of said armature being connected by conductor 13 with the negative pole of battery D2, relay m remaining attracted long enough after the short circuit 43 is closed to permit the locking of relay o. The relay o is included in the conductor 44, and when relay m is inert and relay m energized, it will be included in a circuit. 12', 16, 44, 14, 13, 12. The armature o of relay o is connected with conductor 44 between the `relay o-and armature m2, and is provided with the front contact connected by conductor 45 with the negative pole of battery D2, said conductor including a pair of contacts la? closed by the arm 11, of the trunk selector when away from normal po-- sition. Thus when said armature is attracted, the locking circuit 12', 16, 44,45, 12', is prov1ded for the magnet o, including battery D2. The armature 02 is included 1n conductor 17 which supplies current 'to the operatingl magnets of the hundreds selectora-nd tens and units linder and vwhen said armature is attracted it opens conductor 17 and permits thel restoration of the arms h e2 of the hundreds selector and tens-andunits finder. INhile the selector arms of the hundreds selector and tens-and-units finder-are returning to normal position, current is kept. on the contact a2 forming a terminal of trunk conductor a by the contacts k2 h3 which are maintained closed by the hundreds selector until it returns to normal position, relay m being-denergized to open short circuit 15 immediately after the finder arm af commences its return to zero. When the selector arm kf reachesits normal position, the hundreds selector and tens-andunits finder are free for the servicek of otherv calling subscribers.-

Restoration of individual' distribater.

Y re ay c energized, a short circuit will be esnect a busy tablished about the relay c independent of the previous established short circuit by means of conductors 48, 46, 47. The retraction of armature c2 of relay cdeprives the retaining magnet of current, and selector arms a3 a4 return to resting position, thus releasing trunk c an. Relay c continues in its operated position as long as subscriber remains on the line, or until he begins a new selective operation of his interrupter.` Now when relay c is operated, and relay c is inert, the armature contacts of the two relays combine to consignal apparatus with the line of subscriber A. The busy signal apparatus Z is connected by a conductor 49 with a spring c6 which is adapted to be moved by the armature c* of relay c, when saidarmature is attracted, out of engagement withits contact c", said contact being connected by conductor 50 with the contact cs normally separated from its anvil o9, which is adapted to be 4operated by the armature c5 of relay c when attracted, to unite said contacts of c", contact c being connected with limb 2 of the line. Thus when the relay c is. inert and relay c is energized, a circuit for .the busy signal current rwill be completed by way of conductors 49, 50, line conductor 2, through Vthe substation apparatus to "line conductor 1, and thence through the bridge 3 to ground through the battery D, thus creating a busy signal in the receiver of subscriber A.

When the subscriber A hangs up his telephone, the relay o is dener'gized, and its armature c5 disconnects the signal current from the line and breaks the short circuit about relay c. The same result is accomplished by moving the arm of the interrupter to make a new selection, for the line in that case is oplened at contacts n4 n of the interrupter. T erefore either hanging up or manipulation of the interrupter arm breaks the connection of the busy signal apparatus and prepares the way for a new selection. e

Outline of the ope/ration.

The operation of my system may be briefly described as follows: The subscriber A, to initiate a call, removes his telephone from c in drawin .tively to the hundreds selector,

by the manipulation' Vthe selector arms k away frqm normal its hook, which completes a metallic circuit including battery D and relays c c. Relay up its armature completes a e retaining magnet which in turn connects a test relay e with' theadistributer arm al"` If the first trunk line with which the contact arm as is connected4 is busy, a current from battery D2 connected with said trunk will pass through the test relay e, and so will complete a circuit for the stepping magnet d and advance the distribute arms as a* one step. This operation circuit for t will be continued until the distributer arms make contact with the terminals of a trunk line leading to an idle hundreds selector.

sov

The circuit of conductors 1, 2, is noWeX- tended by way of conductors a', a respecwhereupon relay m of the hundreds selector is operated to complete the continuity of conductor a', and permit the energization of relay m. The rela s p p which are in the bridge of the trung conductors a a, are now operated, but perform no function, since the apparatus controlled thereby is deprived of current until the hundreds selector is operated'. Relay m in drawing up its armature m6 completes a circuit for the steppingand retainin magnets, which advance the hundreds se ector arm one step, or in other words give it an idle onward movement.

Assuming that the called subscriber is No. 4899, the subscriber A will operate his interrupter C to step the' hundreds selector to the terminals representing the hundreds digit of the called line, that is, terminals 48.` In operating the interrupter, the limb 1 of the line is grounded to hold up relays c m and p, and the limb 2 temporarily opened to denergize relay` m. Relay m thereupon retracts its armature whichl permits position ready for operation by the inter- -rupter. The next step in the operation of the interrupter consists in yalternately closing and opening a ground connection to the limb 2 of the llne by means of the ratchet wheel d5 and contact springs d, which serve to alternately open and close contacts m5 m8 of relay m andpcomplete circuits for the stepping and retaining magnets i fn of the hundreds selector. When the contact arm L of the hundreds selector reaches the 48th pair of terminals, the interru ter is restored to normal position and tie metallic circuit again renewed. This allows the relay z' to remain energized an instant, whereupon the connecting magnet 7c of the hundreds selector is allowed to operate, disconnecting the stepping and retaining magnets from the hundreds selector arm` drawing the selector arm L down upon the contact terminals 48. The selector arm la when position, closes contacts h4, and when the connecting magnet is opto return to normal erated contacts h? are closed, so Jfurnishing current from battery D2 to the local circuits of the tens and units finder E. Relay p1 is now operated to complete a circuit for the test relay g2, and in case the first trunk line is engaged, it will close a circuit for the stepping and retaining magnets g q to advance the finder arms e2 successively to the terminals of an idle trunk line. The finder E operates in precisely the same manner as the individual distributer a of the calling line.

' Let us assume that the first idle pair of trunk conductors is 26, 26, leading to tens and units selector B. When the arms e2 are connected with the terminals of conductors 26, 26, a circuit is completed for relay s in the bridge 27 by .Way of trunk conductors26a, 22, a, line conductor 2,to the substation apparatus and back by way of limb 1 of the line through the bridge 3 to the positive pole of battery D. The armature s2 of relay s', in drawing up completes the continuity of conductor 26, 'and applies a test potential from battery D4 to the terminals of this trunk conductor upon the diiferent finders. The completion of the continuity of this conductor allows relay s to operate; The subscriber may now operate the tens and units selector in exactly the same manner as he operated the hundreds selector to bring the contact arms 7' into connection with'the 60th pair of terminals which lead to the substation of the desired line, the connecting magnet u being operated when said connection is completed to draw the arms down against the terminals of the line and to disconnect the stepping and retaining magnets t u from the selector.

When the tens and units selector makes connection with 'conductors 30, 30a, leading to the called station, a circuit is' completed through the relay F, including battery D4, which serves to disconnect the distributer of a called line and its associated apparatus therefrom. The armature F2 of said magnet also connects an impedance coil w in multiple with the relay lw of such line, land the armature F of said relay F includes an impedance coil m in multiple with the relay lw of such line, for `the purpose of balancing the line for transmission purposes as hereinbefore explained.

The subscriber A now signals the called party by depressing his ringing key y, which grounds ing the limb 2 of the line, whereupon relay s, being energized, attracts its armature s3, and relay s being inert, the ringing generator G is connected with the conductor 26n leading to the substation B of the called line, current from said generator flowinlgl over conductors 35, 34, 26a, 30", through t e bell led to connect said hundreds the limb 1 of the line, open at the called station and back over conductors 30, 3, 33, 34:', 3", to earth.

In case the called line is busy, current will be found on the terminals of conductor 30, at the tens and units'selector, and the switching device e'y being operated, such current Would be applied to the relay I, which would short circuit the relays s p m and c, depriving the connecting and retaining'magnets of the selectors, distributer and finder of current, and allowing the distributer, finder and selector arms to return to zero, and in addition applying busyv test to the calling line-under the control or relays c c.

1. In an vautomatic telephone exchange,

the combination with a number of telephone lines extending from substations to a central ofiice, of hundreds selectors at the central office, each having contacts representing the hundreds digits terminals of `said lines, a distributer for each line at the central oflice adapted *toI select an idle hundreds selector,l

station for operating said line with the of the called line, a

means at the calling said selector to connect hundreds digit terminal number of groups of tens-and-units selectors,

the selectors of each group lhaving contacts' representing the tens-and-units digits associated with a given hundreds digit, a finder associated with said hundreds selector adaptwith an idletens-and-units selector having its associated\tensand-units digit terminals thereon, means for operating said distributer and finder, and means at the calling station for operating said idle tens-and-units selectorto complete the connection of the calling line with the desired line.

2. In an automatic telephone exchange, the combination with a number of telephone lines extending from substations to a central oflice, of a source of current in each line at the central office, a switch at the substation of each line.controlling the flow of current therein, a number of hundreds-v selectors at the central office, each having contacts representing the hundreds digits of the lines in the exchange, a' distributer for each line at the central office responsive to the flow ofcurrent in the line, adapted to connect said line with an idle hldidreds-selector, means at a calling station for operating said idle sey lector to connect said line with the contacts digit terminalv operated in making such connection for cutting 0E the idle line terminals ofthe calling line and applying a test potentlal thereto, and means actuated upon the operatlon of the tens-and-units selector for applying a test potential to the remaining line terminals of the called line.

' 4. In an automatic telephone exchange,

the combination with telephone lines extending from substations to a central oflice, of hundreds and tens-and-units selectors at the central office for connecting a calling and a called line, electromagnetic mechanism for operating each connectlng devlce, a magnet I, a circuit therefor completed when connection is completed bysaid tens-and-unlts selector with a busy line, said magnet being adapted to render said electromagnetic mechanism inert, means for restorlng said selectors to normal position, and means actuated when said electromagnetic mechanlsm is rendered inert for applying a busy signal to the calling line.

5. In an automatic telephone exchange, the combination with telephone lines extending from substations to a central ofiice, of hundreds and tens-and-units selectors at the central oflice for connecting a calling and a called line, a relay controlllng each selector, circuits for said relay-controlled from a calling station, a relayI, a circuit thereforcompleted when connection is made by said selectors with a busy line, and shunts about said selector relays closed by said magnet when energized, 'and means for returning said selectors to normal position When their relays are denergized.

6. In an automatic telephone exchange, the combination with telephone lines extend- -ing from substations to a central office, of

hundreds selectors at the central office, a distributer individual to each line adapted to connect the same with an idle hundreds selector, a number of tens-and-units selectors, finders associated with the hundreds selector for connecting the same with an idle tensand-units selector in response to calls, a.re lay for each distributer, selector and finder controlling the operation thereof, c1rcu1ts for said relays controlled from a callin station, a relay I, a circult therefor comp eted a number of when connection is made by the tens-andunltsselector with a busy line, short circuits about the relays controlling the connecting' devices closed by said relay I' when energized to release said connecting devices, means for returning said devices to normal position, and means actuated when said relays are short eircuited for applying a busy signal to the calling line. I .l

In an automatic telephone exchange, .the combination with telephone lines extending from substations to a central ofice, of a number of hundreds selectors at the central ofiice, a distributer individual to each line, and adapted to connect the same With an idle hundredsv selector, a r'elay c controlling said distributer in a circuit controlledfrom the station of such line, tens-and-units selectors, means actuated by a selected hundreds selector for connecting an idle tensand-units selector therewith, relays .controlling said selectors, circuits for said relays controlled from the calling station, means actuated when connection isl made bythe tens-and-units selector withaibusy linebfor rendering said relays inert, means for returning said selectors and distributer to normal position when released,"a relay 'c' in said circuit, and a source' of busy current adapted-to be applied to the calling line by the coperation of' said relays c c. l

8. The combination with a numberl of telephone lines extending from substations to a central office, of a number of hundreds selectors at the central ofiice, an individual distributer for each line at the central,` ofiice,

for operating its distributer to select an idle hundreds selector, each hundreds selector having contacts representing the hundreds digits of the said lines, means controlled from the calling stationgfor operating said idle selector to make connection with the hundreds contact of a called line,

groups of tens-and-ur'iits selectors, the selectors of each group having contacts representing the Vtens-and-units digits associated with a particular hundreds digit, a finder associated with each hundreds digit contact responsive when such contact is connected with a calling line, for connecting the said contact with an idle tens-and-units selector, means controlled from the calling station for operating said idle tens-and-units selector to complete connection with a desired line, and means for establishing a test potential at the contacts of such called line upon the remaining tens-and-units selectors connected therewith.

9. The combination with a number of telephone lines extending from substations to a central oflice, of a number of hundreds to connect said line with an idle hundreds selector, tens-and-units selectors, finders associated with the hundreds' selectors for connecting the same with idle tens-and-units selectors, means controlled from a calling station for operating the selected hundreds and tens-and-units selectors to make connection/ with a called line, and4 mechanism actuate when connection is made with a busy line for applying a busy signal to the calling line and restoring the connecting devices to normal position independent of the calling line. 10. In the combination with a number of metallic circuit telephone llilies extending from substations to a central office, of a number of hundreds selectors at the central o-iice, a dis-- tributer individual to each line adapted to connect such line with an idle hundreds selector, mechanism for operating said distributer controlled from the-station of its line, a number of tens-and-units selectors, a finder associated with the hundreds selector actuated when a calling line is connected thereto for connecting said hundreds selector with an idle tens-and-units selector, mechanism controlled from the calling station for loperating said selected selectors, and a relay in a bridge of the called line adapted to be connected with a source of current by said tens-and-units selector when the same is connected with the called line for temporarily vdepriving the mechanism ci". the individual distributer of the called line of current. y

11. In an automatic telephone exchange, the combination with telephone lines cxtending from substations to a central oiiice, of hundreds and tens-and-units selectors at the central office for connecting a calling and a called line, electromagnetic mechanism for operating each selector controlled from a calling station, means for automatically returning said selectors to normal position when connection is made with a busy line, and means for preventing the access of other calling lines to said selectors until the same have reached their normal positions.

12. The combination with telephone lines extending fromsubstations to a central office, of a number ofline selectors at the central office, each line'selector comprising a contact arm adapted to sweep over line terminals, a distributer individual to each line at the central oiice, a number of trunk lines extending from the contact arm of each selector to a number of individual distributers, means controlled from a calling station for operating its distributer to connect said line with a trunk line leading to an idle selector, means controlled from the calling station for operating the contact arm of the selected selector to make connection with a` desired line, a source of current associated with each selector, means for applying curan automatic telephone exchange,

rent from said source to the other trunk lines connected with said selector the instant said distributer made connection with said trunk line leading to said selector, and normally open contacts closed by said selector arm while away from its normal position for connecting said source with the remaining trunk lines leading to the other distributers associated with said selector.

13. The combination with al calling and a called telephone line, of connecting devices for uniting said lines, a source of current in a branch of the line uniting said stations, a number of relays in multiple between said branch and the connected lines, a condenser interposed between the connection of one of said relays with the line and the point of connection of the other relays, and means actuated when connection is completed between the lines for interposing resistance in multiple with said relay to providean adequate current supply for transmission.

14. In an automatic telephone exchange, the combination with a calling and a called telephone line, of magnetically operated connecting devices and their trunk lines for uniting said lines in metallic circuit, relays for operating said connecting devices, a' source of current in a bridge of the connected lines, condensers in the limbs of the line between the stations,multiple branches of said bridge to both sides of the line including said relays, a multiple branch including a relay being connected with each limb of the line between the condensers and the called station to supply talking current to the called station, a `pairof inductive resistances, and a relay in a circuit closed upon the completion of connection between the lines, for connecting said inductive resistances in multiple with'the relays in the branches supplying current to the called line; whereby an adequate current supply lfor voice transmission is provided.

15. The combination with` a 'number of telephone lines, of distributers, finders and selectors for uniting a calling and a called line, relays c m p s controlling the operation of said distributers, finders and selectors, a circuit for said relays controlled from a calling station, relays 'c m p s in a circuit controlled romthe calling station, means actuated when said distributers, finders and selectors complete their connections for transferring the control of said devices from relays c m p s to relays c mp s, a source of rlnging current, means actuated when relay s is energized and relay s inert for applyin said ringing current to the calling line, an a ringing keyl at the calling station for completing the circuit of relays c m p s and opening the circuits of relays 0 m p 8'; whereby ringing current is applied to the called line and the distributers, finders and selectors held in their operated position. 

